Products > Test Equipment

JunTek PSG9080 Programmable Signal Generator (80 MHz - 300 MSa/s - 14-bit)

<< < (9/31) > >>

TurboTom:
Despite the mechanical deficiencies of this AWG, I wouldn't consider the offset range of +-15V to be the pinnacle to judge about its electrical capabilities. I reason that the output stage (since it apparently consists of a pair of opamps, presumably THS3091) is supplied by +-16V which would result in an output swing of just the +-14.2V measured at high impedance. There's a good reason that other manufacturers limit the high-Z output range of their AWGs to +-10V. They want to make sure that the output doesn't clip... So this may be an indication for bad firmware design but not necessarily for a general inaccuracy.

My approach to evaluate the instrument would be to have a look at the linearity of the DACs. Since they are of the discrete (individual resistors) R-2R type, tolerances in these resistors, especially those close to the MSB, will affect linearity, resulting in harmonic distortion. Moreover, since the R-2R-network is directly driven by the FPGA, all the inaccuracies and the noise superimposed to the FPGA supply rail that feeds the corresponding output bank, will add to the output signal. And then, the internal resistance of the FPGA output drivers adds to the DAC resistors as well. Alltogether, that's what results in a second harmonic of -40dBc as measured by @radiolistener. I'ld also like to see how clean the output is with no apparent signal present, i.e. using a ramp signal at an ultra-low frequency (microhertz) and then analyze the output spectrum. This will show how much noise is being coupled through the FPGA supply (which will probably depend on the momentary output level, i.e. if more of the FPGA outputs are driven high, there's more of the rail noise present than the other way round).

There's a good reason that A- and B-brand manufacturers spend the money on a "real" DAC which could be a considerable fraction of their BOM cost, next to the FPGA.

But to "play fair", I would limit all the testing to the output range that the other instruments can cover, i.e. +-10V High-Z or +-5V @ 50 Ohm load.

And then a look at phase jitter would be interesting. The "easy" way to check for that would be outputting a square wave of an "odd" frequency, triggering the scope on the signal and looking at it with a considerable delay. If the slopes are "smeared out", considerable jitter can be assumed to be present. For proper quantitative measurements, sophisticated frequency counters or a modulation domain analyzer (MDA, i.e. a HP 53310A) are better suited.

A side-by-side comparison against Rigol's entry level AWG which is in the same price range, using all this sophisticated gear, would be quite nice. But I won't be the one to spend the money on this generator, just to do the tests. I can anyway already imagine the results...  ;) -- sorry.  :-//

0culus:

--- Quote from: TheDefpom on September 19, 2020, 09:38:32 am ---
--- Quote from: 0culus on September 19, 2020, 05:16:07 am ---
Just looked at some US sellers of this fine instrument...over $200??? This thing is really a piece of junk. Might be worth $50. My recommendation to anyone looking at these is save your money and get an actual good quality signal generator from a reputable brand.

--- End quote ---

What are you basing this revelation on? have you even used one, or seen one in person ?

I have used one, and I like it, it is a LOT better than some of the others I have tried, and for the money I actually think it is pretty good, it isn't just a function generator, or an ARB, but a SIGNAL GENERATOR.

Not everyone can afford a Keysight, or Rohde & Schwarz etc. that is why there are difference classes of instrument to suit different budgets, for the price class this is in it is excellent.

--- End quote ---

I once had something very similar, and it was a total piece of crap that ended up croaking for no obvious reason (probably the shitty SMPS, not worth fixing). It's not even heavy enough to be a door stop. Notice that I didn't exclude Rigol or Siglent equipment. There also used.

JOHN LEE:
The maximum peak-to-peak value of the output signal of PSG9080 within 1MHz is 25Vpp, and the maximum forward peak value is 12.5V. We set the offset to 12.5V, and it can be seen that it is very accurate; in fact, it can be up to 14V , there is no problem with the parameters. :-+

Johnny B Good:
 Nice review video as per usual, Scott.

 It was interesting to note the lack of anything that looked like a DAC. The resistors on each side of the FPGA look suspiciously like R2R ladder networks. It would be interesting to see what a full amplitude 100KHz sine wave looks like in detail at the half and quarter amplitude points.  :)

 I suspect your mains power arrangement (auto transformer and a UPS being mentioned) may be the reason why you're not seeing the full half mains live leakage on the BNC shields typical of such small class II smpsus, courtesy of the 1 or 2 nF Ycap that diverts the switching noise leakage between the HT and LV windings directly back to their origin in the direct rectified mains HT supply powering the switching chip in that 5v 3A psu board rather than let it take the scenic route and pollute the local environment. You might want to repeat that test whilst plugged directly into an ordinary mains outlet.

 I thought you'd made a rather valid point over taking advantage of the use of an unearthed class II psu to eliminate undesirable earth loops via a noise polluted mains grounding circuit, complete with random DC offsets and switching noise from other smpsu powered kit accompanying the primary 50/60Hz 'hum loop noise' so hated by the audiophool types. ;)

 This was also a desirable feature of Feeltech's FY6600 and predecessor models, provided you never forget the "Ground first, unground last" connection sequence to protect susceptible DUTs from this ESD risk posed by that EMC mandated Ycap which curses all such class II smpsus. Happily, there is a simple way to have your cake and eat it in regard of this conflict of requirements and, funnily enough, the solution is a most superb example of a 'compromise' that gives more benefit than deficit. In this case it's as simple as connecting a 1 to 10 K 'static drain' resistor between the C14's PE tag circuit and the 0v rail of the main board.

 Assuming a 1nF Ycap and 240v 50Hz mains supply, a 10K 'static drain' resistor will knock this 120v (circa 90vac as seen with a typical DMM) leakage voltage down to a mere 377mVac (1K reduces it to 38mVac). If we assume a BNC cord shield resistance as high as one ohm, with a 'static drain' resistance as low as 1K being used to squash the half live mains leakage down to just 38mV or so, this will still provide some 60dB of attenuation to this unwanted ground loop noise pollution. You land up a winner all round - no ESD risk and no perceivable earth loop issue to contend with. ::)

 Incidentally, it's worth pointing out that if you use a typical 5v 3A smpsu wallwart, you'll very likely have exactly the same half mains live voltage issue to contend with even if you've wired that half watt 'static drain' resistor to the PE pin on the C14 socket (unless of course, you've simply switched it off at the back and left it plugged into the mains).

 For anyone looking to expand their hobby interest in electronics and unsure about spending yet another three or four hundred quid on a 'mere signal generator' to go with a recently acquired DSO, these toy generators offer remarkably good value for the money. However, it seems these recent models' improvements over Feeltech's infamous FY6600 have been more by way of show than function as exemplified here with that waste of space front rubber 'bumper' that doesn't even look the part (it looks more like a hideous stage set dressing parody rather than the real thing as seen on mainstream brands).

 Whilst the improved 'haptics' are a long overdue improvement to the user interface (a keypad to directly enter parameter values), the basic electrical performance specs are none to little better that what Feeltech had been offering in their now two year old FY6600 models (and, in many cases, actually worse! :( ), so it's good to see these new contenders vying to displace Feeltech's products as the "Go To" cheap signal generator option being held up to close scrutiny like this. :) :popcorn:

 As for myself, after tinkering with my own FY6600 'tinker toy' for the past twenty months, I'm now rather looking forward to taking delivery of a nice shiny new SDG1032X this coming Monday morning  >:D

John

radiolistener:
just tested frequency meter in PSG9080, it works ok up to 245 MHz. :)

Unfortunately my si5351 cannot produce higher frequency and I don't have signal generator which can produce signal above 245 MHz. But I have UHF transceiver, so I tried to put UHF antenna into BNC connector of PSG9080 and tried to transmit 5W close to antenna. It works!

Frequency measurement of PSG9080 works up to 446 MHz! :)
And probably it may work with even higher frequency, but I don't have source to test it

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod